Well , very aggressive one. I found out, the best to look, when it starts growing, a little ones, and pull them out including root, and than separate it. Sorry. Extremely dangerous. Don't touch it without gloves! Someone posted to a forum, when they walked around a forest, and a woman touched it, she couldn't move in 5 minutes, and ambulance taken her away. Platon a.k.a. Socrates, his figure were killed by the tea or extraction made of it. That was a death penalty in Greece at that time. So if You remove it as soon as it grows, than You have much bigger chance to get rid of it in a couple of years, otherwise as soon as the flower seeds taken by wind all around, it starts growing at autumn more aggressively, so the next spring. Than it floods you area. The big ones usually breaks when You pull it out, and left the root in ground. All other fact written before, are important. Its anti cancer by the way, for centuries, 'doctors' use it against cancer.